Signaling connection admission control in a wireless network

ABSTRACT

A method for admission control of control plane signaling requests includes receiving a signaling request. Upon receipt of the signaling connection request, a first determination is performed to determine whether to provide admission to common resources. When the first determination is negative, a second determination is performed to determine whether to provide admission to dedicated resources. When the second determination is negative, the signaling request is rejected. When the second determination is positive, the request is admitted to dedicated resources. When the first determination is positive, a third determination is performed to determine whether the quality of the signaling request is high or low. If the quality of the request is high, the signaling request is admitted to common resources. When the quality is low, a fourth determination is performed to determine whether to provide admission to dedicated resources. If the fourth determination is positive, the request is admitted to dedicated resources. If the fourth determination is negative, the request is admitted to common resources.

CROSS REFERENCES TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/974,380, filed Oct. 12, 2007, now U.S. Pat. No. 7,583,970, which is acontinuation of U.S. patent application Ser. No. 11/471,454, filed onJun. 19, 2006, now U.S. Pat. No. 7,283,825, which is a continuation ofU.S. patent application Ser. No. 11/042,410 filed Jan. 25, 2005, nowU.S. Pat. No. 7,065,366, which is a continuation of U.S. patentapplication Ser. No. 10/640,291, filed on Aug. 13, 2003, now U.S. Pat.No. 6,868,273, which is a continuation of U.S. patent application Ser.No. 10/264,775, filed on Oct. 4, 2002, which is now U.S. Pat. No.6,631,269, which claims benefit of U.S. Provisional Application No.60/382,811, filed on May 23, 2002, which are incorporated by referenceas if fully set forth herein.

BACKGROUND OF THE INVENTION

The present invention relates to a wireless network where User Equipment(UE) communicates with a radio access network (RAN).

A control plane may be used for all control signaling between the UE andthe RAN. A user plane may be used to transmit and receive all userinformation. Common resources and dedicated resources are defined in acell for the uplink and the downlink transmission between UEs and theRAN. For example, a Random Access Channel (RACH) and a Forward AccessChannel (FACH) could represent common transport channels for the uplinkand the downlink, respectively. The RACH is a contention-based uplinktransport channel, where a dynamic persistence level parameter controlsthe rate at which a UE accesses the RACH.

A UE is said to be in IDLE mode when no connection to the RAN exists,for example, following a power-up of a UE. When a signaling connectionis established, i.e. control plane connection, a UE is said to be inCONNECTED mode. Once in connected mode, both control plane signaling anduser plane information can be exchanged between the UE and the RAN.

An idle mode UE requests a control plane signaling connection bytransmitting a CONNECTION REQUEST message over a common channel, such asthe RACH. An establishment cause may be included in the connectionrequest message to inform the RAN of the reason why the UE is requestingthe connection. The RAN can admit or reject the UE's request for asignaling connection. In the former case, the UE can be admitted forsignaling over common resources (CELL_FACH state) or signaling overdedicated resources (CELL_DCH state). A Call Admission Control (CAC)algorithm may be used to evaluate the allocation of dedicated resourcesfor the uplink and/or downlink transmission between a UE and the RAN.

There is currently, however, no available methods for determiningwhether a UE should be admitted for a control plane signaling connectionand, if admitted, should the UE be admitted for signaling over commonresources or dedicated resources. Some current systems simply alwaysadmit UEs to common resources regardless of the common resources' levelof congestion, thereby arbitrarily increasing congestion and oftencausing the UE to experience significant delay in the exchange ofsignaling information.

A method is therefore needed to determine whether a UE should beadmitted for control plane signaling and, if admitted, whether the UEshould be admitted for signaling over common resources or dedicatedresources.

SUMMARY

The invention is a method for admission control of control planesignaling connection requests. The admission control method determineswhether to accept or reject a UE for a control plane signalingconnection. In the former case, the method determines whether the UEwill be admitted for signaling over common resources or dedicatedresources. In the latter case, the UE is denied access to the networkand remains in its idle state.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a method for admission control of control-plane signalingconnection requests in accordance with the preferred embodiment of theinvention.

FIG. 2 is a method for evaluating whether a signaling connection will beadmitted to common resources in accordance with the preferred embodimentof the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A flow diagram of the method of the present invention is shown in FIG. 1and indicated generally with the numeral 10. The method 10 is forcontrolling control plane signaling connection admission in a wirelessnetwork. The method 10 begins when the RAN receives a control planesignaling connection request from an idle UE (step 12). Admission of thesignaling connection request is first evaluated for whether theconnection should be admitted to common resources (step 14).

Admission to common resources is evaluated based on the predictedcondition of uplink and downlink common resources; in terms of the RACH,(or any equivalent uplink common channel), and the FACH, (or similarlyany equivalent downlink common channel). The admission to commonresources may also be evaluated based on the establishment cause, ifavailable, included in the signaling connection request message. Foreach possible establishment cause, different conditions of RACH and FACHare defined for admission to common resources.

To evaluate the admission of a signaling connection over commonresources (step 14), the method 10 predicts the congestion/performanceof common resources for the admitted UE and all other UEs within thecell that are transmitting over common resources. If the predictedconditions fall below predetermined maximum values, the signalingconnection request is admitted to common resources. If not, thesignaling connection request can be evaluated for admission to dedicatedresources in step 15. An admission for a signaling connection overcommon resources implies that a UE will be in a CELL_FACH statefollowing a connection setup, whereas a UE admitted to dedicatedresources pursuant to a low quality signaling connection will be in aCELL_DCH state following a connection setup.

Where admission to common resources has been denied in step 14, theadmission to dedicated resources is evaluated (step 15) by invoking theCall Admission Control (CAC) method within the RAN. The CAC evaluatesthe possibility of allocating dedicated resources for the exchange ofinformation between the RAN and a UE. When the CAC receives a requestfor resources, it replies by either allocating the requested resourcesor rejecting the request. If the CAC allocates dedicated resources, theUE is admitted for a signaling connection with the allocated dedicatedresources (step 22). Otherwise, the UE is rejected for a signalingconnection (step 21).

In a preferred embodiment, the evaluation of admission to dedicatedresources (step 15) can be establishment cause specific, if theestablishment cause is included in the connection request message. Forexample, for a low priority establishment cause, the admission todedicated resources could be rejected without having invoked the CAC.That is, connection requests that have already been rejected foradmission to common resources in step 14 and have low priorityestablishment causes, may be automatically denied admission to dedicatedresources and thereby rejected.

Where admission to common resources has been granted in step 14, theaccess to common resources is characterized as either high quality orlow quality in step 16. The characterization may be based on factorssuch as delay, interference transmission error rate, congestion,throughput or any other factor allowing the classification of highquality or low quality.

The threshold or criteria for classifying the access of a UE as highquality or low quality may vary as a function of the establishmentcause. Preferably, a lookup table of thresholds for differentestablishment causes are defined. For certain establishment causes, thecriteria for classifying the access of a UE as high quality should bevery broad such that signaling requests containing these establishmentcauses are always classified as high quality thereby ensuring thatdedicated resources will never be requested. Alternatively, for otherestablishment causes, such as the establishment cause that correspondsto an emergency call, the criteria for classifying the access of a UE ashigh quality should be very narrow such that signaling requestscontaining these establishment causes are always classified as lowquality, thereby ensuring that they will be evaluated for admission todedicated resources.

In the high quality case, the UE is immediately admitted for a signalingconnection over common resources (step 20). In the low quality case,however, an analysis (step 18) of whether the UE can be admitted todedicated resources is performed. The analysis (step 18) is performedbecause although the relevant factors for admission to common resourcesare considered acceptable, they are nevertheless sub-optimal making itlikely that the UE will experience transmission errors or significantaccess delays. As a result, the admission for signaling connection overdedicated resources is evaluated in step 18.

The evaluation of whether a low quality signaling connection requestwill be admitted to dedicated resources (step 18) is carried out in thesame manner as in step 15, as described above. In the event the UE isnot admitted to dedicated resources (step 22), however, it will beadmitted for a signaling connection over common resources (step 20).

As mentioned in connection with FIG. 1, step 14 involves an evaluationof whether a UE will be admitted to common resources. A preferred method50 of evaluating whether a signal connection request will be admitted tocommon resources is shown in FIG. 2 and indicated generally with numeral50, where the common resources comprise both the FACH (downlink) and theRACH (uplink), which is a contention-based uplink transport channel.

When evaluating the effect of admission to common resources in terms ofthe RACH, the method 50 evaluates transmission error rates and(optionally) the corresponding delay in successful RACH access. Thefirst step 52 is to calculate the transmission error rate for accessingthe RACH. The transmission error rate for accessing the RACH is observedduring frames preceding the connection request and may be calculatedusing information available at the RAN.

First, the RACH transmission rate and the RACH transmission success rateare calculated by compiling the following information:

-   -   A history of successful RACH transmissions observed over N        frames, where N typically lies in the range of 100.    -   A history of failed RACH transmissions observed over N frames,        where N typically lies in the range of 100.

Accordingly, the following information is all or partially available atthe RAN:

-   -   The establishment cause (IE) in the RRC CONNECTION REQUEST        MESSAGE    -   The rate of successful RACH transmissions, observed over N        frames preceding the connection request where N typically lies        in the range of 100.    -   The rate of failed RACH transmissions, observed over N frames        preceding the connection request where N typically lies in the        range of 100.    -   The dynamic persistence level (DP) parameter which controls the        rate at which UEs access the RACH, if managed at RNC.

The number of RACH accesses attempted by the admitted UE can bepredicted using the establishment cause in the RRC CONNECTION REQUESTmessage. For instance, a UE would use RACH for RAB setup in the case of“Originating Conversational Call” which would typically result in 5 RACHaccesses and 5 FACH accesses in a handshake manner. From the estimatednumber of RACH accesses attempted by the admitted UE, (i.e. the expectedRACH traffic), an estimate in number of successful and failed RACHaccesses and the corresponding transmission error rate within the cellis obtained from basic mathematics/simulations related to the RACHaccess mechanism or system monitoring.

Following step 52, (i.e. once the RACH transmission error rate isknown), there are two possibilities for evaluating if the RACH qualityis sufficient to admit a UE (step 54). The admission may be based on thepredicted delay or the admission may be based on the predicted increasein RACH load. In the former case the delay is calculated based on thetransmission error rate, whereas in the latter case the transmissionerror rate itself is evaluated. Whether admission of a UE is based ondelay or load, is dependent on the establishment cause. For example,delay sensitive connections, such as an originating conversational call,should be admitted based on delay. Other types of requests can beaccepted solely on the expected increase in RACH load.

For signaling requests having establishment causes that require RACHadmission to be based on delay, the method proceeds to step 55. In step55, the resulting delay in accessing the RACH may be calculated usingthe transmission error rate calculated at step 52. The value of thedelay is evaluated in step 56 to determine whether it is below apredetermined maximum value. If, on the other hand, the admission isbased on load (i.e. the delay is not calculated), the transmission errorrate itself is evaluated in step 58 to determine whether it is below apredetermined maximum value. If either of those values (delay ortransmission error rate) is below their respective predetermined maximumvalue, the conditions at the RACH are considered acceptable foradmission to common resources.

A margin is preferably subtracted from a maximum-allowed-value to getthe predetermined maximum value. The margin takes into consideration UEstransmitting/receiving over common resources from neighboring cells thatmight re-select the current cell, a procedure that is assumed to beuncontrollable or at least difficult to control with the UTRAN. In thecases where the idle and connected mode common resources are the same,(i.e. where idle mode and connected mode UEs transmit and receive usingthe same common resources), the method should also consider thetransmission of other RRC connection messages in the margin. Note thatthe predetermined maximum values may vary according to the establishmentcause that is transmitted in the RRC CONNECTION REQUEST message.

Once the effect of admitting a signaling connection request to commonresources has been evaluated in terms of the RACH, it must also beevaluated in terms of the FACH. The factor impacting on common resourcesin terms of the FACH is the amount of congestion at the FACH. In step60, the congestion at the FACH is identified. The amount of FACHcongestion is known at the RAN by the FACH scheduler and the FACH bufferwhich includes the number of FACH messages waiting to be transmitted.The level of FACH congestion is a function of the number of FACHresources, the FACH scheduler design and implementation and the UTRANarchitecture.

Similar to the evaluation of the RACH, following step 60, (i.e. once theFACH congestion is identified), there are two possibilities forevaluating whether to admit a UE based on the identified level ofcongestion (step 62). The admission may be based on the predicted delaythat will result of the identified congestion or the admission may bebased on the predicted increase in FACH load, i.e. the congestionitself. The selection of which method is again dependent on theestablishment cause.

For establishment causes that require the evaluation of FACH congestionto be based on delay, the method proceeds to step 64. In step 64, theresulting delay in accessing the FACH may be calculated using the amountof congestion identified at step 60. The value of the resulting delay isevaluated in step 65 to determine whether it is below a predeterminedmaximum value. If, on the other hand, the admission is based on load(i.e. the delay is not calculated), the congestion itself is evaluatedin step 66 to determine whether it is below a predetermined maximumvalue. If either of those values (delay or congestion) is below theirrespective predetermined maximum value, the conditions at the FACH areconsidered acceptable for admission to common resources and thesignaling connection is admitted to common resources (step 70). As withthe evaluation of the RACH, a margin is preferably subtracted from amaximum allowed value to get the predetermined maximum value.

As can be seen in FIG. 2, if the transmission error rate (step 52) orthe delay caused thereby (step 55) at the RACH are above thepredetermined maximum value, the signaling connection request will notbe admitted to common resources (step 68). Similarly, if the congestion(step 60) or the delay caused thereby (step 64) at the FACH are abovethe predetermined maximum value, the signaling connection request willnot be admitted to common resources (step 68).

As with the criteria for determining high quality and low quality accessin step 16 of FIG. 1, the predetermined maximum value for the parametersat both the RACH and the FACH may vary as a function of theestablishment cause. Therefore, the establishment cause may be used toensure that signaling connection requests having certain establishmentcauses are admitted to common resources regardless of the conditions atthe RACH and the FACH. By way of example, for high priorityestablishment causes such as emergency calls, the predetermined maximumvalue can be very high so that all requests are admitted regardless oferror rates, congestion or the resulting delays caused thereby.

If admission to common resources is denied in FIG. 2, the method shownin FIG. 1 will move from step 14 to step 15 to determine whether therequest may be admitted to dedicated resources and continue as describedabove. Similarly, if admission to common resources is accepted in FIG.2, the method shown in FIG. 1 will move from step 14 to step 16 andcontinue as described above.

Although the present invention has been described in detail, it is to beunderstood that the invention is not limited thereto, and that variouschanges can be made therein without departing from the spirit and scopeof the invention, which is defined by the attached claims.

1. A method for admission control of control plane signaling connectionrequests, comprising: determining admission of a user equipment (UE)tocommon resources upon receipt of a signaling connection request;determining admission of the UE to dedicated resources upon apredetermined event; and allocating one of the common resources or thededicated resources to the UE based on predicted conditions.
 2. Themethod of claim 1, wherein the predicted conditions for common resourcesdetermination include uplink and downlink common resources.
 3. Themethod of claim 1, wherein a positive common resources determinationfurther comprises: determining a signal quality access of the signalingconnection request.
 4. The method of claim 3, wherein a high qualityaccess determination results in allocating the common resources to theUE.
 5. The method of claim 3, wherein a low quality access determinationis the predetermined event.
 6. The method of claim 5, wherein a positivededicated resources determination results in allocating the dedicatedresources to the UE.
 7. The method of claim 5, wherein a negativededicated resources determination results in allocating the commonresources to the UE.
 8. The method of claim 1, wherein a negative commonresources determination is the predetermined event.
 9. The method ofclaim 8, wherein a positive dedicated resources determination results inallocating the dedicated resources to the UE.
 10. The method of claim 8,wherein a negative dedicated resources determination results in denialof resources to the UE.
 11. A radio access network (RAN) for handlingadmission control of control plane signaling connection requests,comprising: the RAN determining admission to common resources uponreceipt of a signaling connection request; the RAN determining admissionto dedicated resources upon a predetermined event; and the RANallocating one of the common resources or the dedicated resources basedon predicted conditions.
 12. The RAN of claim 11, wherein the predictedconditions for common resources determination include uplink anddownlink common resources.
 13. The RAN of claim 11, wherein a positivecommon resources determination further comprises: the RAN determining asignal quality access of the signaling connection request.
 14. The RANof claim 13, wherein a high quality access determination results inallocating the common resources.
 15. The RAN of claim 13, wherein a lowquality access determination is the predetermined event.
 16. The RAN ofclaim 15, wherein a positive dedicated resources determination resultsin allocating the dedicated resources.
 17. The RAN of claim 15, whereina negative dedicated resources determination results in allocating thecommon resources.
 18. The RAN of claim 11, wherein a negative commonresources determination is the predetermined event.
 19. The method ofclaim 8, wherein a positive dedicated resources determination results inallocating the dedicated resources.
 20. The method of claim 8, wherein anegative dedicated resources determination results in denial ofresources.